This invention relates to a magnetic head for use in magnetic recording and reproducing apparatus such as a video tape recorder (VTR), a digital audio tape recorder (DAT) or a hard disk drive (HDD).
In the art of magnetic recording apparatus such as VTRs, recently, the recording density either temporally (e.g. by broadening the frequency band) or spatially (e.g. by decreasing the track width or shortening the wavelength) are increased. Focusing on the shortening of the wavelength, in order to perform shorter-wavelength magnetic recording, it is desirable to use magnetic media having high coercive force. Magnetic heads suitable for use with such high-coercivity media are required to satisfy various conditions including not only the high-frequency characteristics and high wear resistance of the magnetic core (these are the normal requirements to be satisfied by conventional magnetic heads) but also the high resistance to magnetic saturation in the neighborhood of the gap in the magnetic core where magnetic flux is concentrated during recording.
A conventional magnetic head that is known to satisfy these requirements is of a MIG (metal-in-gap) structure which, as shown in FIG. 6, comprises a pair of magnetic core halves 1a and 1b generally that are made of a ferromagnetic oxide having good high-frequency characteristics and that are fitted with thin ferromagnetic metal films 3a and 3b of high saturation magnetic flux density in the gap-forming areas of the core halves 1a and 1b. The pair of the magnetic core halves are joined by a glass 5 which is located near the magnetic gap. The magnetic head in which the interface between the ferromagnetic oxide core halves 1a, 1b and the thin ferromagnetic metal film 3a, 3b is parallel to the gap face 4 is called as a parallel type MIG head. In this parallel type MIG head, the interface defined above acts as a pseudo-gap and this has caused the problem that "beats" occur in the frequency characteristic curve of the reproduction output as shown in FIG. 7. U.S. Pat. No. 4,953,049 proposes that this pseudo-gap problem be solved by a process that comprises grinding and polishing the gap-forming faces of magnetic cores, performing treatments such as phosphate etching and reverse sputtering to have an integral crystal surface exposed on the gap forming faces of the ferromagnetic oxide cores, and forming thin ferromagnetic metal films 3a and 3b on those faces, with intervening thin heat-resistant films 2a and 2b having a thickness of at least 1 nm but not more than a tenth of the gap length.
The aforementioned patent also states that in the case of a single-crystal ferrite being used as the ferromagnetic oxide core material, the effectiveness of the proposed technique depends on the crystal orientation of the ferrite cores and more advantageous results are obtained if the gap-forming faces are {100} planes of a single ferrite crystal than when they are {111} planes. However, a great variety of combinations are conceivable for the crystal orientations of the gap-forming faces and the principal magnetic path forming face, and it is not easy to predict how the reproduction output of the parallel type MIG head or the effectiveness of the proposed method for solving the "pseudo-gap" problem will depend on the crystal orientation of the ferrite cores. Furthermore, very few experimental data have been reported in this regard.
The present inventors made an experiment to find the influence of the pseudo-gap. Two samples of the magnetic head having the construction shown in FIG. 6 are fabricated. One of them was sample A in which the gap-forming faces of the magnetic core halves 1a and 1b were defined by a {100} plane, the surfaces opposing to a recording medium were defined by a {110} plane and the magnetic path forming faces were defined by a {110} plane, so that the &lt;110&gt; direction in the magnetic path forming face of each core half would be parallel to the gap-forming faces, and the other sample was designated B, in which the gap-forming faces of the magnetic core halves 1a and 1b were defined by a {111} plane, the surfaces opposing to a recording medium were defined by 211}{211} plane and the magnetic path forming faces were defined by a {110} plane, and the &lt;110&gt; direction in the magnetic path forming face of one core half would depart from the &lt;110&gt; direction in the magnetic path forming face of the other core half towards the faces in contact with a recording medium. Using those two samples of magnetic heads, the present inventors investigated the magnitude of beats in the reproduced signal, as well as the intensity of the reproduction output. The results obtained are shown in Table 1 below.
In fabricating samples A and B, the two magnetic core halves were joined together at a working temperature of about 700.degree. C. by glass having a softening point of about 600.degree. C., and a substrate film of heat-proof thin film made of SiO.sub.2 that would serve as a pseudo-gap inhibitor was formed in a thickness of 50[nm] at the interface between each of the core halves 1a and 1b and the thin magnetic metal film 3a and 3b.
TABLE 1 ______________________________________ Reproduction Sample Beat (dB) output (dB) ______________________________________ A 0.5 0(Ref.) B 1.2 +2 ______________________________________
As one can see from Table 1, magnetic head sample A produced small beats due to the pseudo-gap but, at the same time, its reproduction output was also small. On the other hand, sample B reproduced a higher output but, at the same time, it produced greater beats due to the pseudo-gap. Thus, it was impossible for the above-described conventional methods to satisfy the following two requirements simultaneously: reducing the intensity of beats due to the pseudo-gap and improving the reproduction output.